Be there as a shoulder to cry on when they’re having a tough time. Offer them advice when they need it and of course, become a secondary author of their most important text messages.

But you know what’s not expected of you? Or even okay for you to do? Slating your best friend’s partner.

We get it, sometimes it’s hard to keep your mouth shut when your friend’s in an argument with their other half. They’re upset and talking negatively about their relationship and all you want to do is back them up by joining in on the slagging match to make them feel better.

Maybe if you’re not actually too keen on their partner, you mean what you’re saying – and it’s a chance to get all of that negativity towards them out of your system.

Maybe you’re only saying it to support your friend – but either way, it’s not okay.

It’s not okay for you to slate your best friend’s partner, regardless of your reasons. While it may be a momentary moment of support for your friend, in the long-run, it’ll only come back to bite you.

While at the time, negativity is what your friend may want to hear to convince them that when it comes to an argument with their partner, they’re in the right; that negativity could end up influencing other decisions that may not be what your friend really wants deep down.

In a time of need, your friend will listen to you and take your advice – and if you’re speaking negatively about their partner they’re more likely to take that on board than to think for themselves. They may end up doing something impulsive like breaking things off in the heat of the moment without thinking clearly about it beforehand.

While this may come as a result of mainly their own decision, if it doesn’t, they might end up regretting their choices and ultimately blaming you for influencing them. And sadly, that’ll be your own fault.

(Picture: Ella Byworth for Metro.co.uk)

Speaking badly about your friend’s partner to them may feel like you’re doing the right thing at the time, and maybe your friend even agrees with you for a brief period – but let’s face it, for most relationships it’s very much an ‘I can say this about my partner but I’ll be mad at anyone else who does so’ approach – just like if someone was to say something mean to your little sibling. It’s fine for you to do so (to an extent), but not for anyone else.

It doesn’t matter how close you are to your friend, nobody likes knowing that their closest mate doesn’t really like their partner. It’s uncomfortable and creates a huge divide between relationships.

So while to you it may seem as though you’re slating their partner to be a support, they may take it as a huge insult towards their partner – and might even start resenting you for it.

And if you’re slating them just because you feel like it and not in an attempt to comfort your friend, that’s even worse. Your friend is with their partner because they like who they are, they have a bond and ultimately they have strong feelings for that person.

Like it or lump it, it’s simply not your place to try to add negativity into the mix. You should be happy for your friend – not trying to sabotage their relationship simply because it doesn’t suit you.

The bottom line is, how would you like it if someone started slating the person you love?

(Picture: Ella Byworth for metro.co.uk)

Insulting your friend’s partner is pretty much insulting your friend’s relationship choices – and that’s pointless and quite honestly not something that falls under the rules of friendship.

You’re not always going to agree on everything – but agreeing to your friend’s relationship shouldn’t even be a subject of conversation.

Not so much because it’s offensive to your friend, but because it could hurt their partner, too. Slagging them off could result in you putting yourself in some not-so-nice situations that may put your friendship at risk.

Think about it: people in relationships share everything – good or bad. You don’t think that once the argument has blown over they’re not both going to come together and talk about what happened? That your friend may not explain to their other half that their words and decisions were strongly influenced by their best friend’s slanted opinion?

You don’t want to be that friend who’s no longer invited to couple-y things simply because you choose not to get along with your mate’s other half, now do you?

It’s so important to a person for their best friend to get along with the person they love, simply because generally, your best friend and your other half are two of the most important people in your life. Slagging them off is completely jeopardising that.

(Picture: Ella Byworth for Metro.co.uk)

Regardless of what you think of them, if they haven’t done anything to intentionally hurt you or your best friend, you have no place to speak badly of them.

You’re not always going to agree on everything when it comes to friendship. That’s life. But that’s also what friendship is partly based on. Not agreeing on everything is what sparks conversation and influences you to think differently and more openly – but some subjects, such as each other’s relationships, should simply be left alone.

Sure, be there to advise your friend on what to do when they’re struggling in their relationship. But make sure that the advice you’re giving is unbiased and isn’t a risk to the relationship itself.

Regardless of what you’re thinking in your head, you can’t be sure that your friend’s upset isn’t a one-off that could easily be resolved.

And you wouldn’t want to be to blame for your friend’s relationship being unnecessarily ruined, now would you?

How to help your friend if they're dating someone genuinely awful:

If your friend is dating someone who is genuinely awful – meaning someone who you really can’t stand for reasons beyond your own personal viewpoint, of course it’s important to talk this through with your friend.

But there are ways to go about it – and slagging them off when your friend’s upset is not one of them.

If you’ve really got a problem with your friend’s partner, sit them down and talk to them about it. Don’t do it when your friend’s feeling vulnerable or is upset and easily influenced.

Show them that you’ve thought about what you’re saying and that you’re not just doing it because you’ve finally found an opportunity to slate the one they love – they’ll appreciate your input much more that way.

Regardless of how they choose to take it on board, talking to your friend about your feelings towards their relationship should only be done when there is a genuine reason for you to be concerned, and not just because your friend’s pissed off at the time.

Because that way, it’ll actually come across as more of an actual concern than you chiming in with an unfair opinion just because you’ve been given half the chance to offer it.